Process for dewaxing hydrocarbon oils



April 1A, 1941.

E, PETTY PRocEss Fon DEWAXING HYDRO'QARBON oILs Filed Jan. 13,' 193:5 2 sheets-sheet 1 Il' .WW YQQQ .All

IN VENTOR faf'/ Paf/y lllfll) All E. PETTY PRocEss Fon DEwAxING HYDRocARBoN oILs April 1, 1941.

Filed Jan. 13, 1935 2 Sheets-Sheet- 2 ATTOR INVENTOR far/ /Dey BY propylene, butylene.

gases at normal temperatures and pressures. By

Patented Apr. 1, 1941 2,236,765 v PRooEss Fon DuwiSNo mnocAnoN Earl Petty, Hempstead, N. Y., assignor, by mesne assignments, to Sun Oil Company, Philadelphia,

Pa., a. corporation of New Jersey Application January 13, 1933, Serial No. 651,497

(ci. iss-1s) 1s Claims.

My invention relates to a novel process for removing wax from a. Wax-oil mixture or removing oil from -a wax-oil mixture. This process is commonly referred to as dewaxing My process takes advantage of the diluent, anti-solvent effect of certain very low boiling hydrocarbons such as propane, butane, ethylene, These hydrocarbons are compressing the hydrocarbons and removing *the heat of compression, it is possible to liquefy them very readily. The liquid hydrocarbon-s have the property of dissolving oil from a wax-oilmxture. At certain temperatures, these hydrocarbons may act as selective solvents in that the oil will be dissolved while the Wax will not. For purposes of clarity, I will refer to the low boil-ing hydrocarbons as propanethough it is to be understood that any suitable hydrocarbons may be used alone or in admixture with carbon disulphlde, sulphur dioxide, methyl chloride, butyl alcohol, or the lik.'

In removing wax from hydrocarbon oil-s, crystallization of the wax in the oil is an important factor. This depends upon the concentration of the solution and the temperature of the mixture.-

By concentration of the mixture is meant the ratio of wax-oil to the diluent. Obviously, 1f

' the oil-Wax is diluted by the addition of the diluent, concentration is varied, i. e. decreased, in such case. Likewise, the removal of heart can be controlled to vary the crystallization conditions.

In considering the crystallization problems which arisein the dewaxing of oil-Wax mixtures, the viscosity effect of the diluent is also an important factor. I have found that generally the lower viscosity will give the better crystal. The dilution requirement in the period of crystal growth is of vital importance. It will be found that too large aV percentage of dilution in the early stages of crystal development will result in the retardation of `crystallization due to the sol-'- vent eiect of the dilluent on the wax. By this I mean that the excess of diluent will redissolve or retard the wax which it is bei-ng attempted to crystallize. I

I have found that, by blendingthe oil-wax mixture with diluen't -to a minimum dilution requireproper concentrations I can obtaina further and i' continued Acrystal growth and separation of wax from the oil-wax mixture by subsequent chillingtemperature lower than the chilled oil-Wax diluentmixture. This further chilling of the propane before dilution of the mixture is necessary to give the proper solidity of crystal so that it can be handled for separation by transfer equipment without redissolving of the wax by the diluent and the oil. to a sufllclently low temperature to act as a diluent without dissolvingthe wax. In other words, at -a suiilclently low temperature, the propane exhibits the properties of a selective solvent, admixing freely with the oil and diluting it while leaving the wax substantially undissolved.

It will be appreciated 'that by chilling an oilwax diluent mixture of a mini-mum concentra-l tion necessary for handling that the wax crystal growth is well started and thatto subsequently obtain 'the proper dilution to facilitate the separa4 tion by the .addition of pre-cooled pnopane,I am enabled. to obtain a more complete and a more expeditious separation of wax from an ollwax mixture than has hitherto been possible. The dilution of the oil-wax mixture is accomplished in a series of stages, as will be hereinafter more fully Pointed out.

In general my invention contemplates the'admixing of propane lor some like liqueed hydrocarbon with an oilawiax mixture in sufficient unantity to give the necessary dilution for handling vthrough :a heat exchanger equipment. The mix ture is iirst chilled by heat exchange with the dewaxed oilgdiluent mixture, the wax-diiuenlt mixture or both. The oil-wax-propane mixture may be then chilled to a lower temperature by one of several methods. I may employ heat exchange through expanding propane or refrigerating gas as a cooling agent. I may expand. propane in direct contact with the oil-wax-propane mixture. The chilled oil-wax-'propane mixture is'then .passed to 4a mixing Meanwhile I separately chill propane to a very low tempera' ture by evaporating a .portion of .the liqueiied propane so that the remainder of the me becomes )chilled by the evaporation I then mix` this f chilled colder -..propane with the pre-cooled oilwax-Jpropane mixture. It will be observed that the addition of .the chilled lpropane has a double effect 6s it will act as a diluent to reduce the concentration of the oil-.wax-propane mixture.. Secondly, because it is so cooled in'and of itself. the temperature of the resulting mixture will greatly lessen. This combination of further chilling and an increase of dilution results in the precipitation of well developed wax crystals and/or amonp ous wax which starts because of the dilution and the low temperature. I then lter the mixture thus prepared. I can precipiand dilution. The subsequent cm1-ung and dilu-v tate more wax and extract more oil by the addi:

non of a umher quantity of chilled diluent to the remainder of the mixture. This results in a fur- The propane ls chilled' ther separation due to` an increase in the dilu;

tion and a decrease in thetemperature. After filtration, I recover the diluent from the oil-d-iluentI and wax-diluent mixtures'frespectively.

In the accompanying drawings which form y part of the instant specification and which are.

*may lbe altered and the temperature lowered at to be read in conjunction therewith and in which like reference numerals are used to indicatelparts inthe various views: v Figure 1 shows a schematicview of one form 36,- and 31 will be allowed to expand and, in so doing, chill the fluid passing through the other side of theheat exchangers.

As pointed out above, the temperature of the oil-wax-propane mixture in pipe 24 will be from OVF. to 20 F.. If desired, the concentration thisvpoint by introducing a portion of the chilled propane from propane evaporator cooler 4 into of apparatus capablefof. carrying out the process of my invention.

Figure 2 shows a schematic view'of another form of apparatus capable of 'i carrying lout the process of my invent-io More particularly referring now to the drawings and especially Figure 1, liquid propane which has been compressed leaves tank I through line 2. A portion of the propane passes through line 3 to a propane evaporator cooler 4. the purpose of which will be hereinafter more fully described. Another portion of the propane passing through line 2 passes through branch line 5 and branch line 6 where it joins the oil-wax mixture coming from tank 1 from which it is being pumped by pump 8 through line 9. The propane from line l 6 and the oil from line 9 admix in line I0 and pass to mixer Il which may be provided with suitable motor driven paddles. -Heat exchangers I2, I3, and I4 permit a pre-cooling of the oilwax-propane mixture. The wax solution, that is the wax-propane mixture, passes from line I5 through heat exchangers I4, I3, and I2. This wax-propane mixture leaves heat exchanger I2 through line I6. At this stage of the process, the

portion of wax-oil and propane is about 1 to 1 by volume. In other words, the oil-wax-propane mixture contains about50% waxy oil and about 50% of propane. The pre-cooled oil-wax-propane mixture leaves heat exchanger I4 through line I1 and passes through heat exchangers I8, I9, `20, 2l, and 22 in succession. The oil solvent mixture coming from the filters through line 23 is from which the gaseous propane is removed through line 28 and passed to compressor 29 in which it is compressed to form a liquid. The liquid is then pumped through line 30, through suitable cooler-condenser 3l, through line 32, to storage tank I. Any ungasifled propane which may escape through line l by priming is separated in separator V21 and returned to theevaporator 4 through line 33. The evaporation of a portion of the body of propane in evaporator 4 serves to coolthe remainder of the propane present in the receptacle. I have found it a very simple matter to chill the body of propane in evaporator cooler 4 to temperatures between and -50 F. A portion of the propane from branch line 5 passes through branch line 34 to heat exchangers 35, 36, and 31. 'Ihese heat exchangers are connected in series, heat exchanger 31 being connected by valved line 33 to the compressor 29. It will be appreciated that the propane passing through the heat exchangers 35,

The oil-wax-propane mixoil-wax-propane mixture flowing in line 24. This can be easily done by means of line 39 which isv orator coolers and is controlled by valve 44. In

the mixing chamber the oil-wax-propane mixture is admixed with a supply of chilled propane from evaporator cooler. It will be recalled that the temperature of the propane is between 40 F.

and F. In lthis mixing chamber 42, the din lution and the lowering of the temperature will cause further solidification of wax crystalsalready formed, the formation of additional .wax

crystals and wash the oil from the wax'. The V mixture leaves the mixing chamber 42 through valved line 45 and passes to filter section 48 Vwhich is provided with a plurality of filter screens' 41. The filtrate passing from filter section 46 through line 48 will have a temperature of about 35 F. and will consistof about `.70% propane and `30% oil. The wax and the oil-wax-propane mixture which contains such wax 4as has not been rendered fllterable leaves filter section 49 through valved line 49 and passesfinto second mixer 50. In the second mixer a. fresh supply of pre-chilled propane passes throughv line 5I which is controlled by valve 52. Here again a fresh crystallization and precipitation takes place due to the continued action of the lowering of the temperature and the decreasing of theA concentration of the oil-wax mixture. The mixture then passes to filter section 53, through valved line 54. The filtrate leaves filtersection 53 through line 55.

' This will have a lower temperature than that leaving the section above. For example, it will be about 37 F. and will consist of about 80% propane and 20% oil. The bottoms from filter section 53 pass through valved line 56 and into mixer 51 where a fresh supply of chilled propane is admixed with the solution. The propane enters the mixer through line 55 which is controlled by valve 59 and communicates with the propane evaporator cooler 4, as will be readily seen by reference to the drawings. The filter area in filter section il to which the mixture now passes through line 6I is somewhat larger than the filter area in the preceding section. The filtrate is removed through lines 62 and 63. It will have a temperature of about 40 F.7and will consist of about propane and 10% oil. It will be noted that in each filtrate withdrawal line 43, 55, 52, and 63, I have placed a three-way cock 64, 55, 66, and 61. The illtrates may be collected in the common line 63 and be passed to filtrate receiver 69. A portion of the nitrate may be collected in receiver 10 from which it may be pumped by pump 1I through line 12 for recycling through line 24.

It will be noted that a line 13 adjoins the three-way cocks 54, 65, and 61. This line acts as a clearing line. By this I mean a line through whichv a menstruum may be circulated to clear the filters. After the device has been in operation for a while, wax will collect on the filter screens. By closing valve 14 and operating pump 18 and setting the three-way cocks, filtrate may be pumped from tank 88 through line 16 to line 13 and thence through the nitrate drawers in reverse direction enabling the filter screens to be cleared. .If desired, gas may be injected.

through line 11 which is controlled by valve 18,

. it being understood of course that the three-way cocks have been'previously set. In this manner, gas will be made to pass through filtrate drawoif lines 48, 55, '82, and'68 to clear the filter screens. It is to be understood, 'of course, that any suitable method of clearing the filter screens may be used: for example, the lter screens may be rotatably mounted adjacent scrubbers so that y, mechanical separation may be resorted to. This is but' a minor detail and forms no major part of the instant invention, though it is essential that the filter screens benot allowed to become clogged. The wax solvent mixture leaves the bottommost lter chamber 88 through valve controlled line 88 and passes into wax-propane mixture tank 8|.

It will be observed that the three iilter sec-l tions 48, 83, and 68 are placed in superposed relationship to form a single column. This is done for purposes of convenience only and it is to be understood that the iter chambers-may be placed in any suitable relationship. The basket centrifuge will remove the crystalline wax which will pass into wax receiver 85 through line 88. 'Ihe wax slurry from the last stage of the lter passes from receiver 8| through line 82 by means of pump 83 and is delivered to basket centrifuge84. In this type machine the granular or crystalline wax can be separated and discharged through pipe 88 into tank 85 and from thence be pumped directly to wax petrolatum stabilizer 88. The remainder of the mixture of wax-propane-oil will leave the basket centrifuge through line 81 and pass into line I5 through heat exchangers i4, I3, and i2 through line i6 to stabilizer 88. Stabilizer-88 is provided with a stripping coil 88 which will strip the propanewaxslurry of the propane which passes through overhead line 88-to cooler 8| and thence to propane tank I. 'I'he mixture of propane and oil and wax combined whichis delivered from"the basket centrifuge as a liquid through the pipe 81 contains mostly propane admixed with some oilv and wax. This mixture can be sent through the exchanger system as indicated and the propane then separated in a1 stabilizer such as .88, or it can be recirculated as blending diluent in mixer to make up part of the original dilution requirement, thus recovering the refrigera- J tion directly instead of through the exchangers and thus saving the step of tie-propanizing, at least part of this wash recovery. The filtrate i'rom tank 88 is pumped normally by pump 15 through line 18 and line 23, it being understood that valve 14 is open and valve 18 is closed.

The oil-propane mixture passing through-line 23 will have a temperature oflbetween \.20 'to '-40 F. The wax slurry passing through line 82 will` have a temperature of about 30 lF.".'I'he oilpropane mixture from line 23 will pass through heat exchangers 22, 2|, 28, I8, and I8, through `line 82to stabilizer 83 which-is provided with a steam' coil 84 which will stripthe propane from the dewaxed oil. .The propane passes overhead' through line 85 where it joins propane from stabilizer 88 in line 88 and is cooled in condenser 8| and passed to storage in propane tank I. The petroiatum wax is withdrawn from stabilizer 88 through line 88 and passed to storage. The dewaxed oil is withdrawn from stabilizer 83 through line 81 and passed to storage.

Referring now to Figure 2, the process is identical with certain minor changes which will 1 now be described. The oil-wax-propane mixture leaving heat exchanger 22 through line 24 passes. into ,Y a crystallizer evaporator |88.l Propanel evaporator cooler 4 is supplied with propane from propane tank I through line 3 which joins line 34. Line 34 is provided with a branch line I8| which is controlled by a valve. 'I'his line supplies propane to crystallizer evaporator |88. 'I'he oil-Wax-propane mixture which passes into crystallizer evaporator |88 through line |83 is diluted with the propane entering through line |8I. By opening valve |84 and allowing a par.- tial -releaseof the pressure, the evaporation of a portion of lthe propane will chill the oil-waxpropane mixture In crystallizer evaporator |88. Ii' desired, a portion of the chilled propane from evaporator cooler 4 may be introduced into crystallizer evaporator |88 through line |85. The chilled oilwaxpropane'.mixture leaves crystallizer evaporator |88 through line |86 and passes to mixer I'81. 'I'his mixer may act as a further crystallizer evaporator, if desired, by the addition of aline |88 provided with a valve |88 opening into a separator ||8 from which the pressure is released. Normally, however, valves I 88 and III are closed so that mixer evaporator |81 acts exactly the same as mixing chamber 42 of Figure 1. It will be observed that line 43 controlled by valve 44 permits the addition of chilled propane tothe mixing chamber |81. The process from here on is identical with that previously. described and like reference numerals willbe used to indicate likeparts as pointed out above.

An oil having a viscosity of 50 at 210 was dewaxed according to my process with the following results:

50 sec. viscosity at 210 F. 94l sec. Viscosity at 130 F, 165 sec. viscosity at 100 F.

I. Charge- Wax component alter removal Oil component after removal l of solv oi so vent Vis. at lm" F, ,seoonds.. 138

Vis at 130 F 0..-. 93 ,Vant 210 F. do.. 56 Vis at 100 F- o 184 Melting point. .F 110-112 Yield .perccnt..v Yield pcrcent.. l0 Cold test -F.. 0

Another oil, which I will'call No. II was dewaxed according to my process with the following results:

n. charge--H 145 sec. @210 F. 1050 sec. at F.

-Wax component alter removal Oil component after removal of solvent oi' solvent Vis. at 210 F .seconds.. 158 v- Yield .peroent.- 8 Melting point ..F 115y No. I oil 1 could not be` dewaxed byv the conven- `tional method. VNo. II oil was dewaxed by the conventional method using narphtha and gasoline as a diluent andchilling followed bla. centrifugal or gravity separation of the wax with the follow-l ing results:

II. By conventional method.

` Charge- 145 sec. at 210 F. 1050 sec. at 100 F.

Pctroiatum wax component ul'tcr Oil component after removal removal oi solvent s vent Yicldf,..... crcent.. 84 Cold testA F. 0.5

material is retained in the wax and causes the low melting point and high viscosity of the wax obtained by my dewaxing process, even though the wax be very concentrated. Pure wax, if completely isolated from the oil, would have a relatively low viscosity, for example, 32-40 sec. at 210 F. In separations which give a large oil loss to the petrolatum, the viscosity of the petrolatum at 210 F. is lowered by the wax viscosity effect. When propane is used, however,

there is a lower oil loss and petrolatum yield. 2

The oil which goes with the wax is of an entirely different series and has such a high viscosity that the low wax viscosity is completely offset.

It will be observed that the distinguishing characteristic of the instant process is the cooling of propane by itself. This cooling is accomplished. it will be observed, by the evaporation of a portion of a body of propane. This chilled propane is then added to an oil-wax-propane mixture of fairly high concentration with the i.'

result that the diluent is increased simultaneously with the lowering of the temperature. I am enabled, by means of this step, to obtain many of the improved results herein pointed out. It

will be observed that I have accomplished the objects of my invention. I am enabled to dewax hydrocarbon oils substantially completely to obtain a very low cold test with ahigh yield of oil.

It will be observed further that pressure is required to keep the propane in a liquid state so that the filtering operation is conducted'under pressure.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further 0bvious that various changes may be made in details Within the scope of my claims Without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited tothe specific details shown and described.

Having thus described my invention, what I claim is:

1. A method of dewaxing hydrocarbon oils, including the steps of diluting a Waxiferous hydrocarbon oil witha hydrocarbon diluent, cooling the mixture without increasing the dilution to a temperature at which wax crystals are developin'g materially, then adding a. hydrocarbon diluent to the mixture, said hydrocarbon diluent being prechilledto a sufficiently low temperature and being added in such quantity as to lower the temperature and increase the dilution of the mixtureat once to a condition where filterable wax crystals are formed and then filtering 'the crystals from the mixture.

2. A method of dewaxing hydrocarbon oils including the steps of diluting a waxiferous hydrocarbon oil with propane, cooling the mixture without increasing the dilution to a temperature at which wax crystals are developing materially, chilling a body of propane to a predetermined lower temperature by evaporating a portion of the same, adding a portionof the body of lchilled propane to the mixture in suicient quantity to simultaneously increase the dilution and lower the temperature of the mixture to cause additional wax precipitation, filtering the mixture to obtain an oil-diluent component and a waxdiluent component. recovering the diluent from the components to obtain a dewaxed oil and wax.

3. A method of dewaxing hydrocarbon oils in which a mixture is formed of wax-bearing hydrocarbon oil and a diluent and the mixture chilled without increasing its dilution to a temperature at which wax crystals are developing materially, chilling a body of liquefied normally gaseous diluent to a temperature lower than the chilled mixture and bringing the chilled oil-wax mixture to a lower temperature by injecting the chilled liquefied diluent whereby additional wax is precipitated.

4. A process of separating ,readily fllterable wax from oils containing wax which comprises. mixing said oil with a liquefied normally gaseous hydrocarbon in an amount sufficient to render the mixture fluent at the dewaxing tempera tures, chilling the mixture to a temperature of about 0J F. or below to precipitate wax, adding sufficient precooled solvent to render the final mixture readily filterable and filtering the precipitated wax from the diluted oil.

5. A process as claimed in claim 4 in which the liquefied normally gaseous hydrocarbon is liquid propane.

6. A process. as claimed rin claim 4 in which the chilling temperature is 10 F. or below.

7. A method of dewaxing hydrocarbon oils including the steps of diluting a waxiferous hydrocarbon oil with only sufficient hydrocarbon diluent to permit handling through heat exchanger equipment, cooling the wax-oil-diluent mixture to a predetermined temperature at which wax crystals are developing materially, separately chilling a body of propane to a temperature below the temperature of the mixture, adding a portion of the chilled propane to the mixture in sufficient quantity to increase the dilution and to lower the temperature of the mixture to precipitate additional wax, filtering the mixture to obtain an oil-diluent component and a wax-diluent component, performing said first mentioned cooling step by passing said first mentioned mixture in heat exchange relation with one of said components and recovering the diluent from the components to obtain a dewaxed oil and wax.

8.1i method of dewaxing hydrocarbon oils including the steps of blending a wax bearing oil with propane to a minimum dilution requirement consistent with the fluidity requirements for handling through heat exchangers, passing the mixture through a chilling zone in indirect heat exchange with colder fluid to thereby chill the mixture to a predetermined temperature at which wax crystals are developing materially, effecting a. decrease in the concentration of the mixture in the later stage of its travel through said chilling zone as compared to the concentration of the mixture in -the early stage of its travel through said zone by adding propane to the mixtureas it enters such later stage, adding to the chilled mixture issuing from said chilling zone colder propane in a quantity sufficient to further solidify the wax' crystals formed and further decrease the concentration of the mixture whereby more expeditious wax separation may be obtained and separating the mixture into an oil-propane component and a waxpropane component.

9. The process of claim 8 in which one of said components is employed as colder iluid in said chilling zone.

10. A method ofv dewaxing hydrocarbon oils including the steps of'blending a wax bearing oil with propane to a minimum dilution requirement consistent with the fluidity requirements for handling through heat exchangers, passing the mixture through a chilling zone in indirect heat exchange with colder fluid to thereby chill the mixture to a temperature at which wax crystals are developing materially, eiecting a decrease in the concentration of the mixture in the later stage of its travel through said chilling zone as compared to the concentration of the mixture in the early stage of its travel through said zone by adding a colder diluent. liquid to the mixture as it enters such later stage, adding to the chilled mixture issuing from said chilling zone colder propane in a quantity suilcient to lfurther solidify the wax crystals formed and further decrease the concentration of the mixture whereby more expeditious wax separation may be obtained, separating the mixture through a chilling zone in indirect heat exchange with colder fluid to therebychill the mixture to a, temperature at which wax crystalssare developing 'materially, adding propane to the, chilled mixture issuing from 'said zone, chilling` the mixture to a lower temperature by evaporating a portion of the propane, chilling the mixture to a still lower temperature to precipitate additional wax by adding separately chilled propane at a temperature lower than the temperature ofthe mixture-and separating an oilpropane component from the mixture..

ture into an oil-propane component and a wax- 4 propane component and recycling to the mixture being chilled a portion of the oil-propane component as said earlier mentioned colder diluent liquid.

11. A method of dewaxing hydrocarbon oils including the steps of blending a Wax bearing oil with propane to a minimum dilution require- X ment, consistent with the iluidity requirements for handling through heat exchangers, passing the mixture through a chilling zone in indirect heat exchange with a colder uid to thereby chill the mixture to a temperature at which wax crystals are developing materially, adding to the chilled mixture issuing from said chilling zone colder propane in a quantity suillcient to furthersolidify the wax crystals formed, *prewax-propane component with the oil to be def' waxed to assist in initially diluting the oil and effect an initial temperature reduction of the'gil by direct heat exchange.

12.l A method of dewaxing hydrocarbon oils in-jg cluding the step of blending a wax bearing oil with propane to a minimum dilution requirement consistent with the uidity requirements for han- 13. A method of dewaxing hydrocarbon oils in cluding the steps of dissolving a wax bearing hydrocarbon oil in a diluent and reducing the temy perature of the mixture by indirect heat exchange t'o a temperature at which wax crystals are developing materially, chilling a body of liquefied, normally gaseous hydrocarbon diluent to a temperature lower than the chilled mixture by evaporating a, portion thereof, and further chilling the partially cooled mixture to a lower temperature by injecting said chilled liquefied hydrocarbon diluent therewith.

14. A method of dewaxing hydrocarbon oils including the steps of forming a mixture of a Waxbearing hydrocarbon oil and a diluent, chilling the mixture to a temperature at which wax crystals are developing materially, bringing the mixture to a lower temperature by injecting thereinto a suicint amount of colder chilled diluent whereby additional wax is precipitated, separating a portion of the wax free oil from the mixture and bringing the mixture to a second and. lower wax precipitating temperature by injecting additional colder chilled diluent thereinto.

15. A method of dewaxing hydrocarbon oils including the steps of diluting a waxiferous hydrocarbon oil with only suiicient diluent to permit handling through heat exchanger equipment, cooling the mixture to a predetermined temperature at which wax crystals are developing materially, further diluting the mixture by addingl thereto a suicient quantity of diluent, said diluent being prechilled to a temperature below the temperature of the mixture, and separating the wax from the mixture.

16. A method of dewaxing hydrocarbon oils including the steps of diluting a waxiferous hydrocarbon oil with only sufficient hydrocarbon diluent to permit'handling through heat exchanger equipment, cooling the mixture to a predetermined temperature at which wax crystals are developing materially, separately chilling a body of propane to a. temperature below the temperature ofthe mixture, adding a portion of the chilled propane to the mixture in suflicient quantity to increase the dilution and lto lower the u temperature of the mixture to precipitate addi- "tional Wax, filtering the mixture to obtain an oil diluent component and a wax diluent component, and recovering the diluent from the components to obtain a dewaxed oil and wax.

17. A method of dewaxing hydrocarbon oils including the steps of cooling a propane wax oil mixture to a temperature at which wax crystals are developing materially, adding to the chilled mixture a propane like diluent chilled below the temperature of the mixture while maintaining the mixture under- -pressure,. separating under pressure a portion of the oil from the mixture, adding additional chilled propane like diluent below the -temperature of the partially de-oiled mixture to the mixture andseparating under dling through heat exchangers, passing the mixg5 pressure additional oil from the mixture.

18. In a method of dewaxing hydrocarbon oils in which a normally gaseous liquefied hydrocarbon is usedas a diluent, chilling an oil-diluent mixture to a temperature at which wax crystals are developing materially, separately chilling'a liquefied normally gaseous hydrocarbon to a temperature below the temperature of the chilled oil-diluent mixture, adding a portion of the 

